全文获取类型
收费全文 | 4619篇 |
免费 | 68篇 |
国内免费 | 143篇 |
学科分类
工业技术 | 4830篇 |
出版年
2024年 | 9篇 |
2023年 | 64篇 |
2022年 | 101篇 |
2021年 | 102篇 |
2020年 | 94篇 |
2019年 | 104篇 |
2018年 | 111篇 |
2017年 | 113篇 |
2016年 | 80篇 |
2015年 | 75篇 |
2014年 | 220篇 |
2013年 | 268篇 |
2012年 | 159篇 |
2011年 | 399篇 |
2010年 | 285篇 |
2009年 | 288篇 |
2008年 | 339篇 |
2007年 | 263篇 |
2006年 | 241篇 |
2005年 | 201篇 |
2004年 | 175篇 |
2003年 | 191篇 |
2002年 | 171篇 |
2001年 | 100篇 |
2000年 | 110篇 |
1999年 | 91篇 |
1998年 | 81篇 |
1997年 | 57篇 |
1996年 | 55篇 |
1995年 | 62篇 |
1994年 | 32篇 |
1993年 | 34篇 |
1992年 | 27篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 26篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有4830条查询结果,搜索用时 15 毫秒
21.
J.H Xiang 《Corrosion Science》2004,46(8):2025-2039
The oxidation of the ternary alloys Ni-45Cu-10Al and Ni-30Cu-10Al has been studied at 800-900 °C under 1 atm O2. The presence of 10 at.% Al reduces significantly the oxidation rate of the corresponding Cu-Ni alloys during the initial oxidation stages, even before the establishment of a complete Al2O3 layer. The weight of individual sample of the two ternary Ni-Cu-10Al alloys at 800 °C increases more rapidly than at 900 °C during the initial oxidation stage. As oxidation proceeds, the weight gain at 800 °C slows down to a degree that the total weight gain after 24 h oxidation at 800 °C is less than that at 900 °C. Due to a faster formation of the Al2O3 layer, which suppresses earlier the further oxidation of Cu and Ni, the external region of the scales grown on Ni-45Cu-10Al contain much less Cu and Ni oxides than those grown on Ni-30Cu-10Al. The transition from the internal oxidation to the selective external oxidation of the most reactive component Al in Ni-Cu-Al alloys is favored by higher values of the Al content, of temperature and of the Cu/Ni ratio. 相似文献
22.
The reduction and subsequent reoxidation of isolated vanadate species supported on silica was investigated using temperature-programmed reduction and oxidation, along with in-situ XANES and Raman spectroscopy. Approximately 70–80% of the vanadium was reduced to V3+ after reduction in H2 at temperatures up to 923 K. Upon reduction, the vanadyl oxygen was removed and the three remaining V–O bonds are lengthened by 0.2 Å. The vanadate species are rapidly reoxidized when exposed to O2, with the amount of oxygen uptake matching well with the amount removed during reduction. In-situ Raman spectroscopy during reoxidation in 18O2 showed that significant scrambling occurs between gas phase oxygen and surface oxygen species during the reoxidation of the vanadate species. 相似文献
23.
On the role of acidity in catalytic oxidation 总被引:2,自引:0,他引:2
The role of the catalyst surface acid-base properties on the heterogeneously-catalyzed oxidation reaction mechanisms is discussed. Acid-base properties depend on the covalent/ionic character of the metal-oxygen bonds and are involved in some steps of the oxidation reactions, such as the activation of the C---H hydrocarbon bonds, the step associated with the evolution of alkoxide species and the desorption/overoxidation of the partial oxidation products. Thus they participate with the cation redox properties in determining the selective/unselective catalyst behavior. 相似文献
24.
The condition of the surfaces is of crucial importance for the deuterium permeation through materials. In this work a study of the surface constants for the adsorption (σk1) and release (σk2) of deuterium under different surface conditions on the martensitic steel DIN 1.4914 (MANET) has been carried out. The growth of an oxide surface layer (Cr2O3) of about 25–30 nm in a MANET sample, heat treated in an oxidizing environment, compared to the bare MANET that have a ‘natural' oxide of about 5 nm has provoked a reduction of both the permeation rate and the recombination coefficient (about 3 orders of magnitude). In addition, the permeation governing process has changed from diffusion-limited to surface-limited. The measurements of the permeation rate of deuterium were performed by a gas-phase permeation technique over the temperature range 574–746 K and for deuterium driving pressures in the range from 3 to 105 Pa. 相似文献
25.
26.
Copolymers of poly(3-hydroxyoctanoate) (PHO) with carboxylic groups in lateral chains have been prepared by chemical modification of unsaturated bacterial polyesters. The oxidation of the pendant alkenes is complete and important loss in molecular weight of polymer was observed. The presence of repeating units containing pendant carboxy groups in the proportion of 25% has enhanced hydrophilicity of these new polymeric structures. Nanoparticles have been prepared from PHO and two functionalized derivatives, characterized by electronic microscopy and compared in view of bioactive molecules transport and release. 相似文献
27.
Partial differential equations, describing the consumption of reactants and the formation of products, have been solved numerically for a step change from inert to reactant feed considering different variants of propene oxidation mechanisms. The response features and their dependency on the rate limiting step have been rationalised in terms of conclusions, which can serve as general guidelines for mechanistic interpretation of experimental transients from hydrocarbon oxidation over metal oxides. Though the response pattern is characteristic of the rate limiting step, it is demonstrated that different variants of mechanisms can give identical response features. In that case complementary investigation with other techniques, or more detailed mathematical analysis is necessary. 相似文献
28.
Chao M. Huang Dong Zhu Xu Yuren Waltraud M. Kriven Chao Y. Yuh 《Materials Science and Engineering: A》1996,220(1-2)
A composite of O′SiAlON (Si2-xAlxN2-xO1+x, with x 0.14) reinforced with 20 vol.% SiC monofilaments was fabricated by hot-pressing, at 1600°C, for 2 h under 34 MPa pressure. The mechanical and interfacial properties of the composites, as-fabricated as well as post-oxidized, were, investigated. The composite exhibited a significant improvement in ultimate flexure strength (640 MPa) and work of fracture (42 kJ m−2) compared with that (350 MPa and 1.8 kJ m−2, respectively) of the monolithic material. These mechanical properties were slightly increased after the composite was heat treated for 24 h in air at 1200 and 1300°C. However, the composite exhibited a significant degradation in ultimate strength, while the work of fracture (WOF) remained unchanged after exposure in air at temperatures beyond 1400°C. The as-fabricated composite revealed a low interfacial shear strength (6.2 MPa) and a frictional sliding stress (3.2 MPa). After the composite was oxidized at elevated temperatures, the interfacial bonding and sliding stresses were reduced to noticeable extents, resulting from the degradation of the carbon coating layer of the SiC monofilaments. 相似文献
29.
The oxidation behavior of a Cu60Hf25Ti15 bulk metallic glass was studied over the temperature range of 375–520 °C in dry air. The oxidation kinetics of the amorphous
alloy generally followed the parabolic law at all temperatures, with an oxidation rate increasing with temperature. The oxidation
rates of the amorphous alloy were much higher than those of polycrystalline pure-Cu, implying that the additions of Hf and
Ti accelerated the oxidation reaction. The composition of the scales formed on the amorphous alloy was strongly temperature-dependent,
since they consisted mostly of Cu4O3 and CuO with minor amounts of HfO2 at T ≤ 450 °C, while mostly CuO with minor amounts of HfO2 and Cu2TiO3 were detected at higher temperatures. In addition, nanocrystalline Cu51Hf14 and Cu3Ti2 phases were detected on the substrate after oxidation at T ≥ 450 °C, indicating the occurrence of phase transformation. 相似文献
30.
~(99)Tc-HMDP和~(99)Tc-HEDP溶液是在相应的螫合剂存在下,用过量SnCl_2还原~(99)TcO_4-制得。用标准I_2液对SnCl_2进行了剩余量电位滴定,确定了在pH~3的介质中,~(99)Tc-HMDP和~(99)Tc-HE-DP中~(99)Tc的氧化态均为+4。全部实验在N_2气流中进行。~(99)Tc-HMDP和~(99)Tc-HEDP的紫外光谱表明:在用I_2滴定的过程中,~(99)Tc只处于一种氧化态+4;将它们放置在空气中,一小时后仍较稳定。 相似文献